1. Field of the Invention
The present invention relates to a high-precision control for the transmission ratio of a toroidal-type continuously variable transmission disposed in a continuously variable transmission for using an automatic transmission apparatus for a vehicle.
2. Description of the Related Art
As an automatic transmission apparatus for a car, use of such a toroidal-type continuously variable transmission unit as shown in FIGS. 13 to 15 has been studied and enforced in part of the car industry. This is referred to as a toroidal-type continuously variable transmission unit of a double cavity type, in which two input side disks 2, 2 are respectively supported on the peripheries of the two end portions of an input shaft 1 through ball splines 3, 3. Therefore, the two input disks 2, 2 are supported in such a manner that they are concentric with each other and can be rotated in synchronization with each other. Also, an output gear 4 is supported on the periphery of the middle portion of the input shaft 1 in such a manner that it can be rotated with respect to the input shaft 1. And, two output side disks 5, 5 are respectively spline engaged with the two end portions of a cylindrical portion formed in the central portion of the output gear 4. Thus, the two output side disks 5, 5 can be rotated together with the output gear 4 and in synchronization with each other.
Also, between the input side disks 2, 2 and output side disks 5, 5, there are interposed and held a plurality of (normally, two or three) power rollers 6, 6, respectively. The power rollers 6, 6 are rotatably supported on the inner surfaces of their associated trunnions 7, 7 through support shafts 8, 8 and a plurality of rolling bearings. The trunnions 7, 7 can be swung (inclined) about and shifted with respect to pivot shafts 9, 9 which are disposed on the longitudinal-direction (in FIGS. 13 and 15, the vertical direction; and, in FIG. 14, the front and back direction) two end portions of their associated trunnions 7, 7 in such a manner that they are concentric with each other. The operation to incline the trunnions 7, 7 is executed by shifting these trunnions 7, 7 in the axial direction of the pivot shafts 9, 9 using actuators 10, 10 each of an oil pressure (hydraulic) type; and, the inclination angles of all of the trunnions 7, 7 are to be synchronized with one another not only in an oil pressure manner but also in a mechanical manner.
That is, in the operation to change a transmission ratio between the input shaft 1 and output gear 4, when changing the inclination angles of the trunnions 7, 7, the trunnions 7, 7 are respectively shifted in the mutually opposite directions, using the actuators 10, 10; for example, the power roller 6 on the right side in FIG. 15 is shifted to the lower side in FIG. 15, while the power roller 6 on the left side in FIG. 15 is shifted to the upper side in FIG. 15. This changes the direction of a tangential-direction force acting on the contact portions between the peripheral surfaces of the power rollers 6, 6 and the inner surfaces of the input side and output side disks 2, 2, 5, 5 (that is, a side slip phenomenon occurs in the contact portions). And, due to this change in the direction of the tangential-direction force, the trunnions 7, 7 are respectively swung (inclined) in the mutually opposite directions about the pivot shafts 9, 9 pivotally supported on support plates 11, 11. This changes the contact positions between the peripheral surfaces of the power rollers 6, 6 and the inner surfaces of the input side and output side disks 2, 5, thereby changing the rotation transmission ratio between the input shaft 1 and output gear 4.
Supply of pressure oil with respect to the actuators 10, 10 is executed using a single transmission ratio control valve 12 regardless of the number of the actuators 10, 10; and, the motion of any one of the trunnions 7 is fed back to the transmission ratio control valve 12. The transmission ratio control valve 12 includes not only a sleeve 14 to be shifted in the axial direction (in FIG. 13, in the front and backdirection; and, in FIG. 15, in the right and left direction) by a stepping motor 13, but also a spool 15 fitted and mounted into the inside-diameter side of the sleeve 14 so as to be shiftable in the axial direction. Also, there are disposed rods 17, 17 which are respectively used to connect the trunnions 7, 7 to the pistons 16, 16 of the actuators 10, 10; and, to the end portion of the rod 17 of any one of the trunnions 7, there is fixed a precess cam 18 and, through the precess cam 18 and a link arm 19, there is formed a feedback mechanism which is used to transmit the motion of the rod 17, that is, the composite value of the axial-direction shift amount and the rotation-direction shift amount to the spool 15. Also, between the trunnions 7, 7, there is provided a synchronizing cable 63; and, the synchronous cable 63 is used to mechanically synchronize the inclination angles of the trunnions 7, 7 with one another.
When switching the transmission condition, using the stepping motor 13, the sleeve 14 is shifted by a given amount to thereby open the flow passage of the transmission ratio control valve 12. As a result of this, pressure oil is fed into the actuators 10, 10 in a given direction, so that the actuators 10, 10 are allowed to shift the trunnions 7, 7 in a given direction respectively. That is, as the pressure oil is fed into the actuators 10, 10, while the trunnions 7, 7 are being shifted in the axial direction of their associated pivot shafts 9, 9, the trunnions are swung about these pivot shafts 9, 9 respectively. And, the motion (the shifting motion in the axial direction and in the swinging direction) of any one of the trunnions 7 is transmitted to the spool 15 through the precess cam 18 fixed to the end portion of the rod 17 and through the link arm 19, then the spool 15 is shifted in the axial direction. Due to this, in a state where the above trunnion 7 is shifted a given amount, the flow passage of the transmission ratio control valve 12 is closed to thereby stop the supply of the pressure oil to the respective actuators 10, 10. Therefore, the axial-direction and swinging-direction shifting amounts of the respective trunnions 7, 7 provide the amounts that correspond to the shifting amount of the sleeve 14 caused by the stepping motor 13.
When putting the above-structured toroidal-type continuously variable transmission unit into operation, one (in FIGS. 13 and 14, the left one) of the input side disks 2 is driven and rotated through such a pressing device 21 of a loading cam type or an oil pressure type as shown in FIGS. 13 and 14, using a drive shaft 20 connected to a power source such as an engine. As a result of this, the pair of input side disks 2, 2 respectively supported on the two end portions of the input shaft 1, while being pressed in their mutually approaching directions, are rotated in synchronization with each other. And, the rotational movements of the input side disks 2, 2 are transmitted through the power rollers 6, 6 to the output side disks 5, 5; and, these rotational movements are then taken out from the output gear 4.
When the power is transmitted from the input side disks 2, 2 to the output side disks 5, 5, with generation of the frictional movements in the contact portions (traction portions) between the peripheral surfaces of the power rollers 6, 6 supported on the inner surfaces of the trunnions 7, 7 and the inner surfaces of the respective disks 2, 5, to these trunnions 7, 7, there is applied a force which goes in the axial directions of the pivot shafts 9, 9 respectively disposed on the two end portions of their associated trunnions 7, 7. This force is referred to as a so called 2 Ft, the magnitude of which is proportional to the torque that is transmitted from the input side disks 2, 2 to the output side disks 5, 5 (or from the output side disk 5, 5 to the input side disks 2, 2). And, such force 2 Ft is supported by the actuators 10, 10. Therefore, when the toroidal-type continuously variable transmission unit is in operation, a pressure difference between a pair of oil pressure chambers 54a, 54b existing on the two sides of the pistons 16, 16 respectively constituting their associated actuators 10, 10 is proportional to the magnitude of the force 2 Ft.
Now, let us assume that the rotation speed between the input shaft 1 and output gear 4 is changed. Firstly, to reduce the rotation speed between the input shaft 1 and output gear 4, the trunnions 7, 7 are respectively shifted in the axial directions of their associated pivot shafts 9, 9 and are swung to such positions as shown in FIG. 14, using the actuators 10, 10. And, the peripheral surfaces of the power rollers 6, 6, as shown in FIG. 14, are respectively contacted with the near-to-center portions of the inner surfaces of the input side disks 2, 2 and the near-to-outer-periphery portions of the inner surfaces of the output side disks 5, 5. On the other hand, to increase the rotation speed between the input shaft 1 and output gear 4, the trunnions 7, 7 are swung in the opposite direction to the direction shown in FIG. 14; and, the trunnions 7, 7 are respectively inclined in such a manner that the peripheral surfaces of the power rollers 6, 6, oppositely to the state shown in FIG. 14, are respectively contacted with the near-to-outer-periphery portions of the inner surfaces of the input side disks 2, 2 and the near-to-center portions of the inner surfaces of the output side disks 5, 5. In case where the inclination angle of the trunnions 7, 7 is set in the intermediate between the above two cases, there can be obtained an intermediate transmission ratio (speed ratio) between the input shaft 1 and output gear 4.
Further, when incorporating the above-structured and -operated toroidal-type continuously variable transmission unit into a continuously variable transmission for an actual car, it has been conventionally proposed to construct a continuously variable transmission apparatus by combining the present toroidal-type continuously variable transmission unit with a differential unit of a gear type such as a planetary gear mechanism. Here, FIG. 16 shows, of the thus-conventionally proposed continuously variable transmission apparatus, a continuously variable transmission apparatus which is disclosed in U.S. Pat. No. 6,251,039B1. This continuously variable transmission apparatus is composed of a toroidal-type continuously variable transmission unit 22 and a planetary-gear-type transmission unit 23. The toroidal-type continuously variable transmission unit 22 comprises an input shaft 1, a pair of input side disks 2, 2, an output side disk 5a, and a plurality of power rollers 6, 6. In the illustrated example, the output side disk 5a has a structure in which the outer surfaces of a pair of output side disks are butted against each other to thereby provide an integral output side disk.
Also, the planetary-gear-type transmission unit 23 includes a carrier 24 connected and fixed to the input shaft 1 and one (in FIG. 16, the right-side) input side disk 2. On the diameter-direction middle portion of the carrier 24, there is rotatably supported a first transmission shaft 26 on the two end portions of which planetary gear elements 25a, 25b are respectively fixedly disposed. Also, there is rotatably supported a second transmission shaft 28 on the two end portion of which sun gears 27a, 27b are respectively fixedly disposed on the opposite side of the input shaft 1, with the carrier 24 between the second transmission shaft 28 and the input shaft 1; and, the second transmission shaft 28 is disposed concentrically with the input shaft 1 and can be rotated. And, the planetary gear elements 25a, 25b are respectively meshingly engaged with a sun gear 30 fixedly disposed on the leading end portion (in FIG. 16, the right end portion) of a hollow rotary shaft 29 the base end portion (in FIG. 16, the left end portion) of which is connected to the output side disk 5a, and the sun gear 27a fixedly disposed on one end portion (in FIG. 16, the left end portion) of the second transmission shaft 28. Also, one (in FIG. 16, the left-side) planetary gear element 25a is meshingly engaged through another planetary gear element 31 with a ring gear 32 which is rotatably disposed on the periphery of the carrier 24.
On the other hand, planetary gear elements 34a, 34b are rotatably supported on a second carrier 33 disposed on the periphery of the sun gear 27b fixedly disposed on the other end portion (in FIG. 16, the right end portion) of the second transmission shaft 28. By the way, the second carrier 33 is fixedly disposed on the base end portion (in FIG. 16, the left end portion) of an output shaft 35 which is disposed concentrically with the input shaft 1 and second transmission shaft 28. Also, the planetary gear elements 34a, 34b are meshingly engaged with each other; and, at the same time, one planetary gear element 34a is meshingly engaged with the sun gear 27b, while the other planetary gear element 34b is meshingly engaged with a second ring gear 36 which is rotatably disposed on the periphery of the second carrier 33. Further, the ring gear 32 and second carrier 33 can be engaged with and removed from each other using a low-speed clutch 37, while the second ring gear 36 and a fixed portion such as a housing can be engaged with and removed from each other using a high-speed clutch 38.
In the case of the above-structured continuously variable transmission shown in FIG. 16, in a so called low-speed mode condition in which the low-speed clutch 37 is connected and the connection of the high-speed clutch 38 is cut off, the power of the input shaft 1 is transmitted through the ring gear 32 to the output shaft 35. And, by changing the transmission ratio of the toroidal-type continuously variable transmission unit 22, the transmission ratio of the whole of the continuously variable transmission apparatus, that is, the transmission ratio between the input shaft 1 and output shaft 35 can be changed. In such low-speed mode condition, the transmission ratio of the whole of the continuously variable transmission apparatus varies infinitely. That is, by controlling the transmission ratio of the toroidal-type continuously variable transmission unit 22, while the input shaft 1 is left rotating in one direction, the rotation state of the output shaft 35 can be switched from the forward rotation state thereof over to the backward rotation state or vice versa with the stop state between them.
By the way, when increasing the speed in such low-speed mode condition or in the constant-speed running operation in such low-speedmode condition, the torque that passes through the toroidal-type continuously variable transmission unit 22 is applied from the input shaft 1 through the carrier 24, first transmission shaft 26, first sun gear 30 and hollow rotary shaft 29 to the output side disk 5a; and, the torque is further applied from the output side disk 5a through the power rollers 6, 6 to the respective input side disks 2, 2. That is, in the speed increasing condition and in the constant-speed running operation, the torque passing through the toroidal-type continuously variable transmission unit 22 circulates in a direction where the input side disks 2, 2 receive the torque from the power rollers 6, 6.
On the other hand, in a so called high-speed mode condition in which the connection of the low-speed clutch 37 is cut off and the high-speed clutch 38 is connected, the power of the input shaft 1 is transmitted through the first and second transmission shafts 26, 28 to the output shaft 35. And, by changing the transmission ratio of the toroidal-type continuously variable transmission unit 22, the transmission ratio of the whole of the continuously variable transmission apparatus can be changed. In this case, as the transmission ratio of the toroidal-type continuously variable transmission unit 22 increases, the transmission ratio of the whole of the continuously variable transmission apparatus increases.
By the way, when increasing the speed in such high-speed mode condition or in the constant-speed running operation in such high-speed mode condition, the torque passing through the toroidal-type continuously variable transmission unit 22 is applied in a direction where the input side disks 2, 2 apply the torque to the power rollers 6, 6.
For example, in the case of a continuously variable transmission apparatus having such a structure as shown in FIG. 16 and capable of realizing a so called infinite transmission ratio in which the output shaft 35 can be stopped while leaving the input shaft 1 rotating, not only from the view point of securing the durability of the toroidal-type continuously variable transmission unit 22 but also from the view point of securing the easy running operation of the car, it is important to maintain the torque applied to the toroidal-type continuously variable transmission unit 22 at a proper value in a state where the transmission ratio is set extremely large. The reason for this is as follows: that is, as can be seen clearly from the relationship [rotation drive force=rotation speedxc3x97torque], in a state where the transmission ratio is extremely large and the output shaft 35 stops or rotates at an extremely low speed while the input shaft 1 remains rotating, the torque passing through the toroidal-type continuously variable transmission unit 22 is large when compared with the torque applied to the input shaft 1. For this reason, in order to secure the durability of the toroidal-type continuously variable transmission unit 22 without increasing the size of the toroidal-type continuously variable transmission unit 22, it is necessary to control the torque so strictly that it is limited to the above-mentioned proper value. Specifically, in order to be able to stop the output shaft 35 while reducing the torque input to the input shaft 1 as much as possible, it is necessary to control the parts including the drive source.
Also, in a state where the transmission ratio is extremely large, even in case where the transmission ratio of the toroidal-type continuously variable transmission unit 22 varies slightly, the torque applied to the output shaft 35 varies greatly. For this reason, in case where the control of the transmission ratio of the toroidal-type continuously variable transmission unit 22 is not executed strictly, there is a possibility that a strange feeling can be given to the driver of the car or the driver can feel it difficult to control the car running operation. For example, in the case of an automatic transmission apparatus for a car, in the car stopping time, while applying the brakes, the driver maintains the car stopping state. In such condition, in case where the transmission ratio of the toroidal-type continuously variable transmission unit 22 is not controlled strictly but a great torque is applied to the output shaft 35, in the car stopping time, there increases the force that is necessary to step down the brakes, which increases the fatigue of the driver. On the other hand, in case where the transmission ratio of the toroidal-type continuously variable transmission unit 22 is not controlled strictly but a torque applied to the output shaft 35 is too small, there is a possibility that the car cannot be started smoothly or the car can back when starting in an uphill slope. Therefore, in an extremely low-speed running time, not only the torque to be transmitted from the drive source to the input shaft 1 must be controlled but also the transmission ratio of the toroidal-type continuously variable transmission unit 22 must be controlled strictly.
In view of the above, in JP-A-10-103461, there is disclosed a structure in which, by controlling directly a pressure difference in an oil-pressure-type (hydraulic) actuator portion for shifting trunnions, the torque passing through the toroidal-type continuously variable transmission unit can be restricted. Also, in JP-A-2001-65676, there are disclosed a structure and a method for controlling the transmission ratio of the toroidal-type continuously variable transmission unit.
In the case of the above structure disclosed in JP-A-10-103461, since the torque is controlled only by the above-mentioned pressure difference, it is difficult to stop the trunnions just when the torque passing through the toroidal-type continuously variable transmission unit coincides with the torque target value. Specifically, because the shifting amounts of the trunnions for controlling the torque become large, there can easily occur a so called over-shoot phenomenon (and further a hunting phenomenon resultant from the over-shoot phenomenon) in which the trunnions do not stop but keep on shifting as they are just when the torque passing through the toroidal-type continuously variable transmission unit coincides with the torque target value, so that the control of the torque passing through the toroidal-type continuously variable transmission unit cannot be stabilized.
Especially, like the ordinary half-toroidal-type continuously variable transmission shown in FIGS. 13 and 14, in the case of a toroidal-type continuously variable transmission unit 22 not having a so called cast angle in which the directions of the pivot shafts 9, 9 respectively disposed on the two end portions of the trunnions 7, 7 are perpendicular to the directions of the center axes of the input side and output side disks 2, 5, the above-mentioned over-shoot phenomenon is easy to occur. On the other hand, like an ordinary full-toroidal-type continuously variable transmission, in the case of a structure having a cast angle, there acts a force going in a direction to bring an end to the over-shoot phenomenon; and, therefore, even in the case of the structure disclosed in the above-cited JP-A-10-103461, it is believed that the torque can be controlled sufficiently.
The present invention aims at eliminating the above drawbacks found in the conventional method and apparatus for controlling the torque and thus the transmission ratio of a toroidal-type continuously variable transmission unit. Accordingly, it is an object of the invention to provide a control method and a control apparatus which, even when used in a continuously variable transmission apparatus incorporating therein a toroidal-type continuously variable transmission unit such as an ordinary half-toroidal-type continuously variable transmission unit not having a cast angle, are capable of controlling strictly the torque that passes through the toroidal-type continuously variable transmission unit.
In attaining the above object, according to a first aspect of the invention, there is provided a control apparatus for controlling transmission ratio of a toroidal-type continuously variable transmission unit of a continuously variable transmission apparatus, the continuously variable transmission apparatus, having: a toroidal-type continuously variable transmission unit including: an input shaft driven and rotated by a drive source; an output shaft; at least a pair of disks supported so as to be relatively rotated with respect to each other and concentric with each other; a plurality of power rollers held between the pair of disks; a plurality of trunnions rotatably supporting the power rollers; and a hydraulic actuator including a pair of oil pressure chambers and causing each of the trunnions to generate a force proportional to a difference between oil pressures within the pair of oil pressure chambers, the toroidal-type continuously variable transmission unit changing a transmission ratio between the pair of disks by shifting the trunnions in the axial direction of pivot shafts as the swing centers of the respective trunnions by using the actuator; and, a differential unit of a gear type including a combination of a plurality of gears, wherein relative shifting speeds between the plurality of gears of the differential unit are changed by adjusting the transmission ratio of the toroidal-type continuously variable transmission unit, thereby the continuously variable transmission apparatus switches the rotation state of the output shaft over between a forward rotation state and a backward rotation state with a stop state between them while rotating the input shaft in one direction by the drive source, and the control apparatus having: rotation speed control unit for controlling the rotation speed of the drive source; transmission ratio setting unit for setting the transmission ratio of the toroidal-type continuously variable transmission unit in order to coincide the rotation speed of the input shaft of the continuously variable transmission apparatus with the controlled rotation speed of the drive source; oil pressure measuring unit for measuring a pressure difference between the oil pressures of the pair of oil pressure chambers of the actuator; and, transmission ratio correcting unit operating in response to a deviation of a pressure difference between a measured value by the oil pressure measuring unit and a target value of a torque passing through the toroidal-type continuously variable transmission unit, and adjusting the transmission ratio of the toroidal-type continuously variable transmission unit so as to eliminate the deviation.
According to the present control apparatus, when an actual measured value of a torque actually passing through the toroidal-type continuously variable transmission unit has a deviation with respect to the target value of the torque and in a direction in such a manner that an input-shaft-side disk of the pair of disks applies a torque to the power rollers, the transmission ratio correcting unit changes the transmission ratio of the toroidal-type continuously variable transmission unit to the speed reducing side, and when the actual measured value of the torque has a deviation with respect to the target value of the torque and in a direction in such a manner that the input-shaft-side disk receives a torque from the power rollers, the transmission ratio correcting unit changes the transmission ratio of the toroidal-type continuously variable transmission unit to the speed increasing side.
Also, the upper limit of the set value of the transmission ratio of the toroidal-type continuously variable transmission unit set by the transmission ratio setting unit is set to the amount corrected in accordance with a deviation between the measured value and the target value of the pressure difference.
Preferably, the control apparatus may further comprise: an electric control circuit for setting the transmission ratio of the toroidal-type continuously variable transmission unit and a target value of a pressure difference based on the target value of a torque passing through the toroidal-type continuously variable transmission unit; and, a hydraulic control circuit for calculating a deviation between the target value and the measured value of the pressure difference by comparing the target value with the measured value and correcting the transmission ratio of the toroidal-type continuously variable transmission unit based on the deviation.
Also, preferably, the control apparatus may further include: a stepping motor for setting the transmission ratio of the toroidal-type continuously variable transmission unit; a differential pressure cylinder for correcting the transmission ratio of the toroidal-type continuously variable transmission unit; a transmission ratio control valve for switching the supply of an oil pressure to the actuator for shifting the trunnions in the axial direction of the pivot shafts; and, a link arm for connecting together the output portion of the stepping motor, the output portion of the differential pressure cylinder, and the transmission ratio control valve.
In the present control apparatus, the transmission ratio control valve is interposed between the stepping motor and the differential pressure cylinder.
Also, the differential pressure cylinder is interposed between the stepping motor and the transmission ratio control valve.
Further, the stepping motor is disposed downward of the differential unit of the gear type.
In the present control apparatus, an elastic member is mounted on at least one of a connecting portion between the link arm and the output portion of the stepping motor, a connecting portion between the link arm and the output portion of the differential pressure cylinder, and a connecting portion between the link arm and the transmission ratio control valve.
And, the elastic member is a plate spring made of metal, the link arm includes a cut-away portion formed in the end portion thereof, a securing pin projected from the output portion of the stepping motor or the differential pressure cylinder or projected from the transmission ratio control valve is engaged into the cut-away portion of the link arm, and a metal spring secured to the output portion presses against the end portion of the link arm to thereby bring the inside edge of the cut-away portion into elastic contact with the outer peripheral surface of the securing pin.
Alternatively, the elastic member is a compression coil spring made of metal, a pair of slide members are fitted with the outer surface of the output portion of the stepping motor or the output portion of the differential pressure cylinder or the transmission ratio control valve so as to be shifted in the axial direction thereof, the pair of slide members respectively include through holes formed in the mutually matched portions thereof, a pivotally supporting pin is projectingly provided on the side surface of the middle portion of the link arm and is inserted through the through holes of the pair of slide members, and the compression coil spring presses against the pair of slide members in approaching directions each other to thereby hold the pivotally supporting pin elastically between the respective inner peripheral surfaces of the through holes formed in the two slide members.
And, in the present control apparatus, when the electric control circuit is at fault, the target value of the torque passing through the toroidal-type continuously variable transmission unit and transmitted to the output shaft is set the maximum value within a restricted range.
Now, according to a second aspect of the invention, there is provided a control method for controlling transmission ratio of a toroidal-type continuously variable transmission unit of a continuously variable transmission apparatus, the continuously variable transmission apparatus, having: a toroidal-type continuously variable transmission unit including: an input shaft driven and rotated by a drive source; an output shaft; at least a pair of disks supported so as to be relatively rotated with respect to each other and concentric with each other; a plurality of power rollers held between the pair of disks; a plurality of trunnions rotatably supporting the power rollers; and a hydraulic actuator including a pair of oil pressure chambers and causing each of the trunnions to generate a force proportional to a difference between oil pressures within the pair of oil pressure chambers, the toroidal-type continuously variable transmission unit changing a transmission ratio between the pair of disks by shifting the trunnions in the axial direction of pivot shafts as the swing centers of the respective trunnions by using the actuator; and, a differential unit of a gear type including a combination of a plurality of gears, wherein relative shifting speeds between the plurality of gears of the differential unit are changed by adjusting the transmission ratio of the toroidal-type continuously variable transmission unit, thereby the continuously variable transmission apparatus switches the rotation state of the output shaft over between a forward rotation state and a backward rotation state with a stop state between them while rotating the input shaft in one direction by the drive source, and the control method, for controlling a torque passing through the toroidal-type continuously variable transmission unit to a target value, having steps of: controlling the rotation speed of the drive source; setting the transmission ratio of the toroidal-type continuously variable transmission unit at a value necessary to coincide the rotation speed of the input shaft of the continuously variable transmission apparatus with the controlled rotation speed of the drive source; measuring a pressure difference between the oil pressures of the pair of oil pressure chambers of the actuator to thereby measure a torque actually passing through the toroidal-type continuously variable transmission unit, calculating a deviation of the torque actually passing through the toroidal-type continuously variable transmission unit with respect to the target value based on the measured and the target value of the torque, and adjusting the transmission ratio of the toroidal-type continuously variable transmission unit so as to eliminate the deviation.
In the present control method, in the range where the torque passing through the toroidal-type continuously variable transmission unit is restricted within the target value, the torque of the drive source for driving the input shaft is changed in a decreasing direction as the rotation speed of the input shaft increases, and when the measured value of the torque actually passing through the toroidal-type continuously variable transmission unit has a deviation with respect to the target value and in a direction where the input-shaft-side disk applies a torque to the power rollers, the toroidal-type continuously variable transmission unit is changed to the speed reducing side, and when the measured value has a deviation with respect to the target value and in a direction where the input-shaft-side disk receives a torque from the power rollers, the toroidal-type continuously variable transmission unit is changed to the speed increasing side.
And, the upper limit of the set value of the transmission ratio of the toroidal-type continuously variable transmission unit necessary to make the torque passing through the toroidal-type continuously variable transmission unit approach the target value is set to the amount corrected based on a deviation between the measured and target values of the pressure difference.
Further, according to the present control method, the setting the transmission ratio of the toroidal-type continuously variable transmission unit necessary to restrict the torque passing through the toroidal-type continuously variable transmission unit to the target value and the target value of the pressure difference based on the torque target value are electrically executed, and the calculating a deviation between the target value and the measured value of the pressure difference by comparing the target value with the measured value, and correcting the transmission ratio of the toroidal-type continuously variable transmission unit based on the deviation are hydraulically executed.
In the case of the above-mentioned control method and apparatus for controlling the transmission ratio of a toroidal-type continuously variable transmission unit for a continuously variable transmission apparatus, control for restricting the torque passing through the toroidal-type continuously variable transmission unit to the target value is executed in two stages. Thanks to this, while preventing the over-shoot phenomenon (and further a hunting phenomenon resultant from the over-shoot phenomenon) from occurring, or while, even when the over-shoot phenomenon (and further the hunting phenomenon) occurs, controlling it down to a practically negligible level, the above torque can be restricted to the target value.